Fibronectins were isolated from both bovine colostrum and fresh milk, and they were found to be very similar to plasma fibronectin. The concentration of fibronectin in milk decreased post partum: 30 micrograms/ml after 0 d and 2 micrograms/ml after 7-851 d. No fibronectin could be detected in any brands of ultra heat treated liquid milk on the market (less than or equal to 0.006 micrograms/ml).